Duplicating a movie strip in the VSE
If you look at the info panel when you shift+D you do get that python there, but that only duplicates the strip and snaps it to the end of the first strip. If you move it to above the existing strip, it also uses bpy.ops.transform.seq_slide(value=(-26,1)) where -26 is to move the strip the number of frames of the strip(original is 26 frames) and the 1 is positive direction next channel. If you automate it, you will need to have the python look get the number of frames of the strip and use that where the -26 is.